Ryan,
Take a look at Kent's Bike Blog
http://kentsbike.blogspot.comI know he rode from western WA to Banff as a warm-up for the Tour Divide
one year. There might be route details in the blog archive. The good
folks at Adventure Cycling Association can probably help you as well.
People do ride US 97/97A down from Penticton; You might also be able
to research coming down through Invermere on 93/95 and then west on
US 2 by Sandpoint, ID towards Wenatchee and then meet the 97. I've
only done these as a driver and if it were me I'd look into ACA routes
and maps to minimize highway time through these corridors.
There have been a lot of major forest fires in N. Central WA this summer;
recent rainfall has knocked them back a bit and so hopefully smoke won't
be severe by when you start. Something to research a bit more once you've
picked a route.
Safe travels!
-tabby